1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus of operating in an idle mode in a wireless communication system.
2. Related Art
With the development of communication and the spread of multimedia technology, a wireless communication system uses various techniques for massive data transmission. A method of assigning a more number of frequency resources may be used as a method of increasing radio capacity. However, since the number of frequency resources is limited, there is a limitation when the more number of frequency resources are assigned to a plurality of users. As one of methods for effectively utilizing the limited frequency resources, there is a method of utilizing a small-sized cell. With the small-sized cell, a base station (BS) provides a service to a less number of users, and thus the BS can assign a more number of frequency resources to the users. Further, a service for massive data transmission with better quality can be provided to the plurality of users.
When a user equipment (UE) does not transmit or receive data for a specific period of time, the UE transitions to an idle mode for power saving. The UE in the idle mode may periodically wake up from a state of not receiving a transmit (Tx) signal of the BS in order to receive a paging message or a broadcast message, and determine whether to transition to an active mode. The UE in the idle mode announces a location of the UE to a core network of a wireless communication system by performing a location update process. The location update process of the UE may be classified into: (1) timer based location update; (2) paging group based location update; and (3) power down based location update, etc. The timer based location update is a method in which location update is performed when a location update timer of the UE expires. The paging group based location update is a method in which location update is performed when the UE moves to an area of another paging group other than a paging group of the UE. The power down based location update is a method in which location update is performed before power is turned off by the UE. The core network can recognize a correct location of the UE according to the location update of the UE, and can transmit the paging message for the UE.
The UE monitors the paging message according to a paging cycle and a paging offset. The paging offset is a period in which the paging message is transmitted. The paging offset is a time at which the paging message is transmitted in one paging cycle. If there is no paging message transmitted to the UE in a current paging cycle, the UE continuously monitors whether the paging message of the UE is transmitted in a next paging cycle.
The paging message is transmitted over a resource region pre-defined according to the paging offset. However, an essential message to be transmitted on a real-time basis such as a voice over Internet protocol (VoIP) message may be transmitted over a resource region pre-defined for the paging message. In this case, the UE cannot receive the paging message of the UE in the current paging cycle and thus has to receive the paging message in the next paging cycle. As a result, transmission delay may occur when the paging message is transmitted to the UE.
Accordingly, there is a need for avoiding the transmission delay of the paging message and for flexibly transmitting the paging message.